The principal objective of the proposed research is to study the visual inputs in a central visual processing area of the brain. The optic tectum of a lower vertebrate, the leopard frog, will be used as a model system. Retino-tectal input will be distinguished from, and compared to, other visual input in the superficial layers of the tectum. There are four specific aims: 1) Using anatomical and physiological techniques, the origin and distribution of non-retinal visual inputs to frog superficial tectum will be determined; 2) the nucleus isthmi, a tegmental visual area which is connected exclusively to the tectum will be electrically stimulated to study the effects on tectal elements; 3) the nature of visually driven ipsilateral isthmo-tectal units will be studied using extracellular microelectrode recording in the tectum. These recordings will be compared with cases where n. isthmi has been temporarily silenced by application of a local anesthetic; 4) the origin of cholinergic tectal elements will be studied by measuring tectal choline acetyltransferase activity and the rate of tectal acetylcholine synthesis in normal, optic nerve cut, and n. isthmi ablated animals. In addition, the effects of the tectal application of various cholinergic agonists and antagonists will be studied while n. isthmi is electrically stimulated. The long-term objective of this study is to determine how visual information is integrated in order to further our understanding of the central processes of vision.